1. Field of the Invention
This invention relates to a network management technique, and more particularly to an ATM (Asynchronous Transfer Mode) exchange system and a switching control method for a permanent virtual connection (hereinafter referred to as “PVC connection”) for an ATM network.
2. Description of the Related Art
As diversification, increase in speed and increase in capacity of services in an ATM network in recent years proceed, it becomes a significant subject to improve an ATM exchange system in terms of the performance, function and reliability. As a necessary function, it is demanded particularly to augment the reliability of a PVC connection. Specifically, when a trouble occurs with a circuit, it is significant to continue communication of a PVC connection with a minimum cell loss.
As a method of preventing disconnection of a PVC connection by a trouble of a circuit or an apparatus, it is a possible idea to employ a redundant configuration (dual configuration, n+1 multiple configuration) in hardware for a circuit itself. This method, however, is disadvantageous in that it requires complicated maintenance.
As another method, it is known to use a network management system (NMS) to automatically or manually switch, when a trouble occurs with a PVC connection, the PVC connection to another PVC connection of another route (refer to, for example, Japanese Patent Laid-Open No. 2000-59374). With the method, however, when a trouble occurs or upon release from a trouble, it is necessary for the network management system to notify each ATM exchange of setting/deletion of a PVC connection. Therefore, the method has a problem in that considerable time is required for the exchanging process. Further, if a trouble occurs with the network management system, then this makes setting itself of a PVC connection impossible.
Thus, a method has been proposed wherein network management is performed autonomously and discretely without depending upon a network management system. For example, Japanese Patent Laid-Open No. 266480/1997 discloses a method wherein, when a trouble occurs with a circuit, a routing function of a switched virtual connection (SVC) is used to set a bypassing SVC connection.
Meanwhile, Japanese Patent Laid-Open No. 215148/1999 discloses another method wherein both of a PVC connection and an SVC connection are used such that, if a trouble occurs with the PVC, a call setting procedure by the SVC is executed to set an optimum SVC connection as a bypass link.
However, with the conventional autonomous PVC bypassing method, however, when a trouble occurs with a currently used PVC connection, a bypassing SVC connection is searched for and set. Therefore, rapid switching cannot be anticipated. Further, although a bypassing connection is set and switchably used when a trouble occurs with a currently used connection and then the bypassing connection is disconnected and the currently used connection is switchably used upon release of the currently used connection, the conventional autonomous PVC bypassing method does not propose any autonomous countermeasure of software against occurrence of/release from a trouble which may occur with the currently used or bypassing connection.